Biological Effects of Radiation Flashcards
What are the three electron interactions with matter?
Ionisation
Excitation
Heat production
What is the energy loss of an electron for each ionisation caused?
34eV
State and explain the three light production methods on irradiation
Fluorescence: prompt light emission
Phosphorescence: delayed light emission
Thermoluminescence: light emission when heated
Explain how indirect damage can arise from radiation.
Action of radiation leads to excited macromolecules (RH -> RH*) and then to the production of free radicals R· and H·
Which is more likely at diagnostic levels: direct or indirect action?
Indirect
Define Linear Energy Transfer (LET)
LET is a measure of the rate at which energy is transferred to the medium (ie. ionisation density along the track of the particle)
A more penetrating beam has a lower LET
Define Radiobiological Effectiveness (RBE)
RBE = dose of 200kVp x-rays/dose of other radiation to give same biological effect
What does RBE vary with?
Dose
Dose rate
Fractionation
Physiological conditions (eg O2 concentration)
Biological species
Biological end point chose for comparision
Time after irraditaion when measurements made